Motor stalls when braking hard

Sounds like the rear float level is set too high.Fuel is splashing out the vent tube into the carb inlet.Does it act like it's flooded when you go to start it back up?

Carb is set right also it starts just fine. This one has me stumped. Any other ideas ?

Thanks Jim

This might be a really stupid post but you are stumped so here goes. Does the car stall when it is at idle and you apply the brakes hard like a panic stop? Pinched wire or something electrical?

sudden vacuum demand on booster....vacuum leak?


[This message has been edited by RoBeRt (edited 05-14-2004).]

The plot thickens,at speed with the brakes applied hard the motor stalls just before a complete stop, not when rolling. I do not have a vacuum gauge but I soaped the conections and see no bubbles brakes on or off. Jim

Your NOT going to see any bubbles with a vacumn leak; as NO air is coming out! Atmospheric Pressure IS going in! I'am with RoBeRt, it sounds like a ruptured Brake Booster Diaphram. You'll have to borrow a Vacumn Gauge. Your Vacumn at idle (1000 RPM) should be between 15 and 17 Inches of Mercury. Mine is 19-20. If you are lower than 15 Inches I would suspect a Vacumn leak; also, a rising and lowering needle with-in a range of 5-10 Inches, would indicate a Vacumn leak. Could also be a short in the brake lights, effecting the ignition, BUT that should blow the fuse! Could also be WHERE you have the Ignition 12 Volts, wired to? And if you are using a Ballast resister (wire or ceramic block), or not. As the brake lights could draw off current from the Coil or Ignition box or both. Anything is possible with these Machines. As mention above, could even be fuel!! Either Fuel bowl level or the Idle screws are screwed IN to far. Good-Luck with it! And let us know how you make out. Marlin.

An easy way to tell if it is the brake booster is to disconnect it at the manifold and plug it .Drive the car(be carefull)and see if it still does it .The brake pedal will be hard .

One way I've heard of to check for vacuum leaks is to spray starting fluid on the connections, you'll hear a marked increase in speed if the connection is leaking.

This may seem over simple, but have you checked your oil level? If it is too low it could slop away from the pick up during hard braking and cause the engine to stall from low oil pressure.

I have the same problem. Been that way since the 3yrs I've had the car. I have the vent whistles and everything, doesn't help. I've got a 10yr old Holley 700DP on mine, and am hoping that at some point when I switch to a more modern carb, it aleviates this problem.

Problem over set rpm @ 1200 must be low vacuum because of my cam Thanks Jim

Stalling during a panic stop is usually one of two things: either fuel is slopping out of the float bowl vents and flooding the engine or the engine is starving due to fuel slosh in the bowls. Neither are easy to diagnose since both are transient problems that happen only when the car is rolling. To fix the first, traditionally one takes a piece of tygon tubing and joins the float vents in a fairly tall loop, with a single venting hole in the top of the loop, up inside the air cleaner opening. The second required jet extensions, or turning the carb(s) sideways or stuffing blocks inside the bowls to control slosh. If your problem is something else, first look very closely at your motor mounts, to be sure the rubber isolaters aren't deteriorated or the mounting bolts broken, allowing the engine to shift under braking. Both are common & either can cause all sorts of bad-news re stretched wires, cracked hoses etc.